An electromagnetic coil, or simply a coil, is formed when an electrical conductor, such as e.g. a copper wire, is wound to create an inductive or electromagnetic element. Thereby the wire may also be wound around a core or form. One loop of wire may be referred to as a turn, and a coil comprises one or more turns. Coils serving as inductors are wide-spread in electronic circuits as a passive two-terminal electrical component that stores energy in its magnetic field. For example, coils may be used for realizing transformers for transferring energy from one electrical circuit to another by inductive coupling without moving parts. Also, coils may be used to build resonant circuits comprising serial and/or parallel arrangements of inductors and capacitors. In some applications coils may also serve as antennas or antenna-like elements for detecting electromagnetic fields, such as e.g. in Radio Frequency Identification (RFID) or similar applications.
In one of such applications, for example, it is proposed to detect a transition of a moving playing object, such as a ball or a puck, through a detection plane (e.g. a goal plane) using electromagnetic fields and/or signals. In some ball sports, as e.g. soccer or football, the usage of automated goal-detection systems is discussed in order to avoid human wrong decisions. Thereby the so-called goal-line technology is a technology, which can determine when the ball has crossed the goal line, assisting the referee in calling a goal or not. There are various alternative approaches for determining the exact position or location of the ball, such as video-based or electromagnetic field based systems. In an electromagnetic field based system a moving object, such as a ball, may be equipped with electronic circuitry for transmitting and/or receiving and/or reflecting electromagnetic signals. For such electromagnetic approaches electronic components are required inside the ball, wherein the size of the electronics may differ depending on its functionality and the used frequency range. For small and medium-sized systems the electronic may be installed within the ball's center, for example. For goal-detection systems requiring more area and volume, as e.g. for systems using magnetic fields in the sub-MHz range, the required loop antennas and/or the further electronic components may be installed on the circumference of the ball.
For achieving detection properties which are possibly rotationally invariant, one goal-detection system proposes to install three orthogonally placed coils or loop-antennas within or on a moving object, e.g., a ball, for emitting or reflecting at least a portion of an electromagnetic field. Due to this orthogonal arrangement of the coils the rotational position of the ball only has little influence on the electromagnetic emission or reflection properties, as in theory the three orthogonal loop-antennas always amount to an effective loop-antenna, whose effective opening surface is perpendicular to an incident magnetic field coming from a transmitter installed at or near the goal. That is to say, the normal of the effective opening surface is essentially parallel to the magnetic field vector.
For a correct functioning, i.e. high precision, of goal-detection systems electromagnetic properties of the ball or a puck are a crucial criterion. In one exemplary goal-detection system 800 (see FIG. 8a) a magnetic field {right arrow over (H)} may be generated by means of a current-carrying conductor embracing a goal frame 802. The generated magnetic field {right arrow over (H)} is thereby perpendicular to a detection plane 804 defined by the goal frame 802. This stimulating magnetic field {right arrow over (H)} is reflected by the ball 806, wherein the reflected signal {right arrow over (H)}B should generate the same directional vector as the stimulating field {right arrow over (H)} (due to the ball electronics with a shifted phase). The geometric accuracy of the reflected signal directly influences the measurement result and, hence, the accuracy of the goal decision.
The detection system 800 is based on three orthogonal coils 808-1, 808-2, and 808-3 in the ball 806 (see FIG. 8b). Each of the coils 808-1, 808-2, and 808-3 may comprise a plurality of turns which may, for example, be inserted in between the ball bladder and the ball hull or cover. For avoiding any irregularities in the ball hull the inserted coils 808-1, 808-2, and 808-3 should be rather flat between the ball bladder and the ball hull (i.e. the ball cover). Hence, the windings or turns of the coil should be arranged possibly side-by-side along the circumference of the ball 806.
The fabrication of items of sports equipment or playing equipment, such as balls, being equipped with more or one coils or loop-antennas, in particular arranged on its circumference, is relatively cumbersome. Furthermore, the exact positioning of the coils within or around the ball is crucial. It is desirable to provide a concept of how the at least one coil or loop antenna may be designed and how it may be integrated into the item of sports equipment in order to withstand mechanical and/or elastic deformations of the deformable item of sports equipment, for example, when hit from a player or shot against an obstacle, such as a goal frame, for example.